U.S. patent number 7,102,797 [Application Number 10/150,932] was granted by the patent office on 2006-09-05 for image reading device and image forming apparatus including the image reading device.
This patent grant is currently assigned to Ricoh Company, Ltd.. Invention is credited to Yoshihiro Sakai.
United States Patent |
7,102,797 |
Sakai |
September 5, 2006 |
Image reading device and image forming apparatus including the
image reading device
Abstract
In an image reading device having a sheet-through mechanism, a
controller controls a stepping motor to decelerate an image reading
system when the image reading system is moved to a reference white
plate reading position, and controls a stepping motor drive
electric current to decrease when the image reading system reads a
reference white plate. When the image reading system finishes
reading the reference white plate, the controller controls the
stepping motor drive electric current to increase so as to rapidly
decelerate the image reading system. The controller further
controls the stepping motor such that a moving speed of the image
reading system to an original document reading position is lower
than a moving speed of the image reading system to the reference
white plate reading position.
Inventors: |
Sakai; Yoshihiro (Tokyo,
JP) |
Assignee: |
Ricoh Company, Ltd. (Tokyo,
JP)
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Family
ID: |
18995451 |
Appl.
No.: |
10/150,932 |
Filed: |
May 21, 2002 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20020186426 A1 |
Dec 12, 2002 |
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Foreign Application Priority Data
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May 21, 2001 [JP] |
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2001-150446 |
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Current U.S.
Class: |
358/461; 358/406;
358/474; 382/274 |
Current CPC
Class: |
H04N
1/1008 (20130101); H04N 1/1013 (20130101); H04N
1/193 (20130101); H04N 2201/044 (20130101); H04N
2201/04755 (20130101) |
Current International
Class: |
H04N
1/00 (20060101); G06K 9/40 (20060101); H04N
1/04 (20060101); H04N 1/40 (20060101) |
Field of
Search: |
;358/461,406,474,496,497,486 ;382/274 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Grant; Jerome
Assistant Examiner: Safaipour; Houshang
Attorney, Agent or Firm: Oblon, Spivak, McClelland, Maier
& Neustadt, P.C.
Claims
What is claimed as new and is desired to be secured by Letters
Patent of the United States is:
1. An image reading device comprising: an image reading system
configured to read an image on a document; a stepping motor
configured to apply a drive force to the image reading system to
move the image reading system; a controller configured to control
the stepping motor to drive in accordance with speed patterns of
the stepping motor set for each operation of acceleration, moving
at constant velocity, and deceleration of the image reading system;
a document feeder configured to feed the document to a
predetermined document reading position where the image reading
system is held stationary to read the image on the document fed by
the document feeder; and a reference white plate configured to be
read by the image reading system at a reference white plate reading
position spaced apart from the document reading position in a
moving direction of the image reading system before reading the
image on the document using the image reading system to form a read
image so as to correct a white level of the read image on the
document, wherein the controller controls the stepping motor to
drive the image reading system to move to the reference white plate
reading position for reading the reference white plate while
moving, and then controls the stepping motor to decelerate the
image reading system when the image reading system is moved to the
reference white plate reading position such that the image reading
system reads the reference white plate only during the deceleration
of the image reading system before reading the image on the
document.
2. The image reading device according to claim 1, wherein the
controller controls a stepping motor drive electric current to
decrease when the image reading system reads the reference white
plate.
3. The image reading device according to claim 1, wherein when the
image reading system finishes reading the reference white plate,
the controller controls a stepping motor drive electric current to
increase so as to rapidly decelerate the image reading system.
4. The image reading device according to claim 1, wherein the
controller controls the stepping motor to drive the image reading
system to move to the document reading position for reading the
image on the document fed by the document feeder after reading the
reference white plate by the image reading system, and controls the
stepping motor such that a moving speed of the image reading system
to the document reading position is lower than a moving speed of
the image reading system to the reference white plate reading
position.
5. An image forming apparatus, comprising: an image reading device
including: an image reading system configured to read an image on a
document; a stepping motor configured to apply a drive force to the
image reading system to move the image reading system; a controller
configured to control the stepping motor to drive in accordance
with speed patterns of the stepping motor set for each operation of
acceleration, moving at constant velocity, and deceleration of the
image reading system; a document feeder configured to feed the
document to a predetermined document reading position where the
image reading system is held stationary to read the image on the
document fed by the document feeder; and a reference white plate
configured to be read by the image reading system at a reference
white plate reading position spaced apart from the document reading
position in a moving direction of the image reading system before
reading the image on the document using the image reading system to
form a read image so as to correct a white level of the read image
on the document, wherein the controller controls the stepping motor
to drive the image reading system to move to the reference white
plate reading position for reading the reference white plate while
moving, and then controls the stepping motor to decelerate the
image reading system when the image reading system is moved to the
reference white plate reading position such that the image reading
system reads the reference white plate only during deceleration of
the image reading system before reading the image on the document;
and a printer device configured to print the image of the document
read by the image reading device.
6. The image forming apparatus according to claim 5, wherein the
controller controls a stepping motor drive electric current to
decrease when the image reading system reads the reference white
plate.
7. The image forming apparatus according to claim 5, wherein when
the image reading system finishes reading the reference white
plate, the controller controls a stepping motor drive electric
current to increase so as to rapidly decelerate the image reading
system.
8. The image forming apparatus according to claim 5, wherein the
controller controls the stepping motor to drive the image reading
system to move to the document reading position for reading the
image on the document fed by the document feeder after reading the
reference white plate by the image reading system, and controls the
stepping motor such that a moving speed of the image reading system
to the document reading position is lower than a moving speed of
the image reading system to the reference white plate reading
position.
9. An image reading device comprising: reading means for reading an
image on a document; applying means for applying a drive force to
the reading means to move the reading means; controlling means for
controlling the applying means to drive in accordance with speed
patterns of the applying means set for each operation of
acceleration, moving at constant velocity, and deceleration of the
reading means; feeding means for feeding the document to a
predetermined document reading position where the reading means is
held stationary to read the image on the document fed using the
feeding means; and reference white plate means to be read by the
reading means at a reference white plate means reading position
spaced apart from the document reading position in a moving
direction of the reading means before reading the image on the
document by the reading means so as to correct a white level of the
read image on the document; wherein the controlling means controls
the applying means to drive the reading means to move to the
reference white plate means reading position for reading the
reference white plate means while moving, and then controls the
applying means to decelerate the reading means when the reading
means is moved to the reference white plate means reading position
such that the reading means reads the reference white plate means
only during deceleration of the reading means before reading the
image on the document.
10. The image reading device according to claim 9, wherein the
controlling means controls a stepping motor drive electric current
to decrease when the reading means reads the reference white plate
means.
11. The image reading device according to claim 9, wherein when the
reading means finishes reading the reference white plate means, the
controlling means controls a stepping motor drive electric current
to increase so as to rapidly decelerate the reading means.
12. The image reading device according to claim 9, wherein the
controlling means controls the applying means to drive the reading
means to move to the document reading position for reading the
image the document fed by the feeding means after reading the
reference white plate means by the reading means, and controls the
applying means such that a moving speed of the reading means to the
document reading position is lower than a moving speed of the
reading means to the reference white plate means reading
position.
13. An image reading method comprising: moving an image reading
system to a reference white plate reading position; decelerating
the image reading system when the image reading system is moved to
the reference white plate reading position; reading the reference
white plate with the image reading system only during the
deceleration of the image reading system; moving the image reading
system to a document reading position; and reading an image on a
document using the image reading system after the reading of the
reference white plate.
14. The image reading method according to claim 13, wherein the
step of reading the reference white plate includes controlling a
stepping motor drive electric current to decrease.
15. The image reading method according to claim 13, further
comprising decelerating the image reading system rapidly by
controlling a stepping motor drive electric current to increase
when the image reading system finishes reading the reference white
plate.
16. The image reading method according to claim 13, wherein the
step of moving the image reading system to the document reading
position includes moving the image reading system to the document
reading position at a lower speed than moving the image reading
system to the reference white plate reading position.
17. The image reading device according to claim 1, wherein the
controller is configured to control the image reading system to
read the reference white plate only during the moving of the image
reading system at constant velocity, when the image is read on the
document that is stationary.
18. The image reading device according to claim 1, wherein the
controller is configured to control the image reading system to
read the reference white plate only during the moving of the image
reading system at constant velocity before the image is read on the
document that is stationary.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
This application contains subject matter related to and claims
priority, under 35 U.S.C. .sctn.119, from Japanese Patent
Application No. 2001-150446, filed in the Japanese Patent Office on
May 21, 2001, the entire disclosure of which is hereby incorporated
by reference herein.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to an image reading device
that reads image data of an original document with an image sensor
and an image forming apparatus, such as a digital copying machine,
a laser beam printer, a facsimile machine, etc., that forms an
image based on the image data output from the image reading device
and more particularly, to a control of reading operation of a
reference white plate for obtaining shading data in the image
reading device having a sheet-through mechanism.
2. Discussion of Background
An image reading device used in a widespread digital copying
machine, a scanner, or other similar image forming apparatus, may
employ a method of reading an image of an original document by a
two-dimensional scanning in which a charge-coupled device (CCD)
line sensor is moved in a sub-scanning direction perpendicular to a
main scanning line relatively to an original document illuminated
by a lamp.
The image reading device employing such an image reading method in
which the CCD line sensor is moved relatively to the original
document, generally uses two types of image reading mechanisms. One
type of image reading mechanism may be referred to as an image
reading system moving mechanism in which an image of an original
document set on an original document setting table (e.g., a contact
glass) in a stationary state is read by moving an image reading
system. Another type of image reading mechanism may be referred to
as a sheet-through mechanism in which an original document is fed
by an original document feeding device (hereinafter simply referred
to as a "document feeder") so as to pass through a stationary image
reading system including a CCD line sensor. An image of an original
document is read by the stationary image reading system while
moving the original document relative to the image reading
system.
Recently, an image reading device often has both of the
above-described two types of image reading mechanisms. Hereinafter,
a description will be made to an image reading device that reads an
image of an original document by both of the two types of image
reading mechanisms.
The image reading device having both of the two types of image
reading mechanisms reads an image of an original document by a
common image reading system. When performing an image reading
operation in the sheet-through mechanism, the image reading
operation is performed in a condition that a movable image reading
system is held stationary at a predetermined image reading position
provided at a part of an original document conveying path in a
document feeder. In the image reading device having both of the two
types of image reading mechanisms, it is not desirable that an
output of image read by the image reading system moving mechanism
is different from that of image read by the sheet-through mechanism
or an output of image read by either of the two image reading
mechanisms changes with time. Therefore, in order to stabilize
outputs of read images, an image reading system reads a reference
white plate before reading an image of an original document to
obtain a reference white level or shading data based on the data of
read reference white plate. A white level of image data of a read
original document is corrected using the shading data.
In the image reading system moving mechanism, following a reading
operation of a reference white plate arranged between a home
position of an image reading system and a position where an
original document is set on a contact glass, an image reading
operation of the original document is performed.
In the sheet-through mechanism, as described above, an image
reading system reads an image of a moving original document fed by
a document feeder in a condition that the image reading system is
held stationary at a predetermined image reading position.
Therefore, when reading the same reference white plate also used in
the image reading system moving mechanism, the image reading system
needs to be moved to the position where the reference white plate
is arranged. This results in adding a step of moving the image
reading system contrary to the aim of eliminating the necessity of
moving the image reading system in the sheet-through mechanism.
Accordingly, in order not to reduce the advantage of high
throughput in the sheet-through mechanism allowing an image reading
device to read original documents consecutively, it may be desired
to reduce a whole period of time required for performing the
reading operation of the reference white plate as much as
possible.
In the above-described image reading device, a carriage carrying
the image reading system is driven to move by a stepping motor.
Generally, an image reading operation is controlled to be performed
when the movement of the carriage changes to a constant velocity
movement after being accelerated from a stop position of the
carriage. Subsequently, the movement of the carriage is controlled
to be decelerated after the image reading operation. Such a control
operation is performed in both of an image reading operation of an
original document and a reading operation of a reference white
plate.
FIG. 7 is a velocity chart illustrating a control of movement of a
carriage and a control of reading operation of a reference white
plate according to a background art. With regard to a timing of
reading a reference white plate according to a background art, a
reading operation of the reference white plate is performed in an
area indicated by a reference character "A" in FIG. 7 in which the
carriage moves at a constant velocity and vibrations of an image
reading system carried by the carriage are the weakest after the
carriage is driven to move by a stepping motor and is accelerated.
Alternatively, in order to reduce a time of reading the reference
white plate as much as possible, the reading operation of the
reference white plate is performed in an area indicated by a
reference character "B" in FIG. 7 in which the carriage is
accelerated, with some disadvantages such as vibrations of the
image reading system.
Recently, demands have been increasing for an image reading
performance satisfying both high speed and high image quality such
as an image reading speed of 40 sheets/minute and a resolution of
1200 dpi, for example, in a color image reading device. In such a
color image reading device, if a reading operation of a reference
white plate is performed in the area "A" in FIG. 7, it takes time
until vibrations of an image reading system become weak, and a
start of the reading operation is delayed, thereby increasing a
whole period of time required for performing the reading
operation.
If the reading operation of the reference white plate is performed
in the area "B" in FIG. 7, the reading operation can be started
earlier than in the area "A". However, there may be a high
possibility of occurrence of error in data of the read reference
white plate due to the vibrations generated when the carriage is
driven to move from a stop position. As a result, it may be hard to
obtain appropriate shading data.
SUMMARY OF THE INVENTION
According to one aspect of the present invention, an image reading
device includes an image reading system configured to read an image
of an original document, a stepping motor configured to apply a
drive force to the image reading system so as to move the image
reading system, a controller configured to control the stepping
motor to drive in accordance with speed patterns of the stepping
motor set for each operation of acceleration, moving at constant
velocity, and deceleration of the image reading system, an original
document feeder configured to feed an original document to a
predetermined original document reading position where the image
reading system is held stationary to read an image of the original
document fed by the original document feeder, and a reference white
plate configured to be read by the image reading system at a
reference white plate reading position spaced apart from the
original document reading position in a moving direction of the
image reading system before reading the image of the original
document using the image reading system to form a read image so as
to correct a white level of the read image of the original
document. The controller controls the stepping motor to drive the
image reading system to move to the reference white plate reading
position for reading the reference white plate while moving, and
then controls the stepping motor to decelerate the image reading
system when the image reading system is moved to the reference
white plate reading position.
Objects, features, and advantages of the present invention will
become apparent from the following detailed description when read
in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWING FIGURES
A more complete appreciation of the present invention and many of
the attendant advantages thereof will be readily obtained as the
same becomes better understood by reference to the following
detailed description when considered in connection with the
accompanying drawings, wherein:
FIG. 1 is a schematic perspective view of a carriage driving system
of an image reading device according to an embodiment of the
present invention;
FIG. 2 is a side view of a part of the image reading device
illustrating a schematic construction of an image reading system
according to the embodiment of the present invention;
FIG. 3 is a block diagram illustrating a structure of a stepping
motor drive control system in the image reading device according to
the embodiment of the present invention;
FIG. 4 is a chart illustrating an example of a speed pattern of a
stepping motor for a movement control of carriages in an image
reading system moving mode;
FIG. 5A is a schematic view of main elements of the image reading
device according to the embodiment of the present invention;
FIG. 5B is a velocity chart illustrating a movement control of the
carriages in a sheet-through mode;
FIG. 5C is a velocity chart illustrating a movement control of the
carriages in the image reading system moving mode;
FIG. 6 is a schematic vertical longitudinal sectional side view of
an image forming apparatus including the image reading device of
FIG. 1 according to another embodiment of the present invention;
and
FIG. 7 is a velocity chart illustrating a control of movement of a
carriage and a control of reading operation of a reference white
plate according to a background art.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Preferred embodiments of the present invention are described in
detail referring to the drawings, wherein like reference numerals
designate identical or corresponding parts throughout the several
views.
FIG. 1 is a schematic perspective view of a carriage driving system
of an image reading device according to an embodiment of the
present invention. FIG. 2 is a side view of a part of the image
reading device illustrating a schematic construction of an image
reading system.
Referring to FIGS. 1 and 2, an image reading device 50 includes a
first carriage 1 that carries an exposure lamp 14 that irradiates
an image surface of an original document with light and a first
mirror 15 that reflects the light reflected from the image surface
of the original document, and a second carriage 2 that carries a
second mirror 16 and a third mirror 17 that reflect the light
reflected from the first mirror 15. The light reflected from the
third mirror 17, corresponding to the image of the original
document, is imaged on a charge-coupled device 19 (hereinafter
referred to as a CCD 19) serving as an image sensor through an
imaging lens 18. In this embodiment, the first carriage 1 and the
second carriage 2 and the above-described elements carried by the
first and second carriages 1, 2 are defined as an "image reading
system" as a whole.
Referring to FIG. 1, the image reading device 50 further includes a
pair of wires 3, a drive shaft 4, a pair of wire pulleys 5
integrally provided on the drive shaft 4, idle pulleys 6a, 6b, 6c,
and 6d, a timing belt 7, a stepping motor 8, timing belt pulleys 9
and 10, a detection part 11 provided on the first carriage 1, and a
home position sensor 12 that detects the detection part 11 of the
first carriage 1.
Referring further to FIG. 2, the image reading device 50 further
includes a contact glass 13 serving as an original document setting
table, a stepping motor drive control board 21 that controls the
stepping motor 8 to drive, a scanner control board 20 that controls
image processing and the stepping motor drive control board 21, and
a reference white plate 22 used for obtaining shading data.
A brief description will be made to an operation of a carriage
driving system referring to FIG. 1. The drive force of the stepping
motor 8 is transmitted to the first carriage 1 and the second
carriage 2 via the pair of wires 3 opposing each other and being
extended at both respective sides of the first carriage 1 and the
second carriage 2 in a main scanning direction indicated by arrow
in FIG. 1. The wires 3 are driven by the pair of wire pulleys 5
integrally provided on both sides of the drive shaft 4 in the main
scanning direction. The wire pulleys 5 are driven by the timing
belt pulley 10 integrally provided on a shaft of the stepping motor
8 via the timing belt pulley 9 provided on one end of the drive
shaft 4 and via the timing belt 7 spanned around the timing belt
pulleys 9 and 10.
When turning on a power supply switch (not shown), in order to
accurately locate the first carriage 1 and the second carriage 2 at
respective home positions, the stepping motor 8 starts to drive the
drive shaft 4. Then, the drive force of the stepping motor 8 is
transmitted to the first carriage 1 and the second carriage 2 via
the wires 3, thereby causing the first carriage 1 and the second
carriage 2 to move in a forward direction indicated by the arrow in
FIG. 1. After moving a predetermined distance in the forward
direction, the first carriage 1 and the second carriage 2 start
moving in a return direction indicated by arrow in FIG. 1. When the
home position sensor 12 detects the detection part 11 provided on a
lower part of the first carriage 1, the first carriage 1 and the
second carriage 2 move further in the return direction by a
predetermined distance corresponding to predetermined pulses, and
stop moving at respective stopping positions. These respective
stopping positions of the first carriage 1 and the second carriage
2 correspond to their home positions. The first carriage 1 and the
second carriage 2 are in a standby condition at the respective home
positions, and start reading operations from the respective home
positions upon receiving a reading instruction.
In this embodiment, the image reading device 50 has two types of
image reading mechanisms such as an image reading system moving
mechanism and a sheet-through mechanism. Therefore, a document
feeder 30 (illustrated in FIG. 5A) integrally formed with a platen
plate (not shown) is provided above the contact glass 13 so as to
cover and uncover the contact glass 13. The platen plate serves to
cover an original document set on the contact glass 13 and press
the original document against the surface of the contact glass
13.
The image reading device 50, according to the embodiment of the
present invention, includes a construction similar to that of a
background image reading device that reads an image of an original
document by two types of image reading mechanisms. In FIG. 2, a
construction of the image reading device 50 above the contact glass
13 is omitted, so that the document feeder 30 is not shown. The
image reading device 50 having the two types of image reading
mechanisms reads an image of an original document by use of a
common image reading system. When performing an image reading
operation in the sheet-through mechanism, the image reading
operation is performed in a condition that a movable image reading
system is held stationary at a predetermined image reading position
provided at a part of an original document conveying path in the
document feeder 30. The details of the image reading operation in
the sheet-through mechanism will be described in more detail below
referring to FIG. 5B.
Next, a description will be made of a control of the stepping motor
8 for driving the first carriage 1 and the second carriage 2.
FIG. 3 is a block diagram illustrating a structure of a stepping
motor drive control system in the image reading device 50. The
stepping motor 8 is controlled to be driven by the stepping motor
drive control board 21. The scanner control board 20, including a
central processing unit (CPU) that controls the whole image reading
device 50, generates control signals, such as a stepping motor
drive clock, forward/reverse signals, drive electric current
switching signals, etc., based on control data, such as speed
patterns of the stepping motor 8 set for each operation of the
image reading system of the image reading device 50. The
above-described control signals, such as the stepping motor drive
clock, the forward/reverse signals, the drive electric current
switching signals, etc., are input to the stepping motor drive
control board 21. The stepping motor drive control board 21
controls the stepping motor 8 to drive by changing the drive
electric current passing through each phase of the stepping motor 8
in accordance with the above-described control signals.
The speed of the stepping motor 8 is determined by the frequency of
drive clock or the number of drive pulses per unit of time (pulse
per second). The phase switching timing of the stepping motor 8 is
controlled based on the frequency of drive clock. As the frequency
of drive clock increases, the speed of the stepping motor 8
increases, and as the frequency of drive clock decreases, the speed
of the stepping motor 8 decreases. Therefore, various kinds of
acceleration and deceleration of the stepping motor 8 are achieved
by controlling the frequency of drive clock. The drive electric
current for the stepping motor 8 is controlled to be switched
depending on the operations of the first and second carriages 1, 2,
such as acceleration, deceleration, reading operation, return,
wait, etc.
Next, a description will be made of a drive control of the first
carriage 1 and the second carriage 2 at the time of a reading
operation of the image reading device 50. FIG. 5A is a schematic
view of the main elements of the image reading device 50. FIG. 5B
is a velocity chart illustrating a movement control of the carriage
in a reading mode by the sheet-through mechanism. FIG. 5C is a
velocity chart illustrating a movement control of the carriage in a
reading mode by an image reading system moving mechanism.
Hereinafter, the reading mode by the sheet-through mechanism may be
simply referred to as a "sheet-through mode", and the reading mode
by the image reading system moving mechanism may be simply referred
to as an "image reading system moving mode".
In this embodiment, the second carriage 2 moves together with the
first carriage 1 in the sub-scanning direction at about one-half of
the moving speed of the first carriage 1. Therefore, hereinafter,
the drive control of the first carriage 1 and the second carriage 2
at the time of the reading operation of the image reading device 50
may be described referring to the first carriage 1 as a whole.
Referring to FIG. 5A, the first carriage 1 carrying the exposure
lamp 14 and the first mirror 15 is in a standby condition at a home
position. The first carriage 1 moves from the home position to
three different reading positions. Specifically, the first reading
position is located at a position most close to the home position
of the three reading positions. Further, the first reading position
is located in a part of an original document conveying path in the
document feeder 30 provided above the contact glass 13. The first
reading position is indicated as an "image reading position in a
sheet-through mode" in FIG. 5A. At the first reading position, the
first carriage 1 held in a stationary state reads an image of an
original document being conveyed in the original document conveying
path in the document feeder 30.
The second reading position is located at some midpoint of movement
of the first carriage 1 in the forward direction indicated by the
arrow in FIG. 5A from the home position. At the second reading
position, the first carriage 1 reads the reference white plate 22
provided at a part of the contact glass 13 while moving.
The third reading position is located at a position farthest away
from the home position in the forward direction. The third reading
position is indicated as an "image reading position in an image
reading system moving mode" in FIG. 5A. The third reading position
corresponds to a reference position of an original document where a
leading edge of an original document is set on the contact glass
13. At the third reading position, the first carriage 1 reads an
image of an original document set on the contact glass 13 in a
stationary condition while moving.
Hereinafter is described an operation of the image reading device
50 in an image reading system moving mode. When a start key (not
shown) is pressed after setting an original document on the contact
glass 13 and closing the platen plate, a drive clock is output from
the scanner control board 20 to the stepping motor drive control
board 21 at a predetermined timing, thereby driving the stepping
motor 8. The drive controls of the first and second carriages 1, 2,
are performed based on the speed patterns of the stepping motor 8
set for each operation of the image reading system of the image
reading device 50. FIG. 4 is a chart illustrating an example of a
speed pattern of the stepping motor 8 for the movement control of
the first and second carriages 1, 2, in the image reading system
moving mode.
As illustrated in FIG. 4, the stepping motor 8 causes the first
carriage 1 to move from an accelerated condition to a constant
velocity condition. Because the first carriage 1 reads an image of
an original document from the leading edge (i.e., a reading start
position) to the trailing edge in a constant velocity period, the
velocity of the first carriage 1 should be stabilized in the
constant velocity period. Before reading an image of an original
document, the first carriage 1 needs to read the reference white
plate 22 so as to obtain shading data.
The timing of reading the reference white plate 22 will be
described referring to FIG. 5C. As illustrated in FIG. 5C, the
first carriage 1 starts to move in the forward direction by driving
the stepping motor 8, and moves from an accelerated condition to a
constant velocity condition. The reading operation of the reference
white plate 22 is performed in a stable constant velocity period
after an unstable variable velocity period immediately after a
velocity transitionary period. In the image reading system moving
mode, an image reading operation of an original document is
performed following the reading operation of the reference white
plate 22. Therefore, the reading operation of the reference white
plate 22 is also performed in a part of the stable constant
velocity period for reading an image of an original document.
The reflected light from the reference white plate 22 is led to the
CCD 19 through the imaging lens 18. The reflected light is
converted into an electric signal by the CCD 19. The data of the
reference white plate 22 obtained by the CCD 19 is transmitted to
the scanner control board 20 and is subjected to image processing.
Consequently, a reference white level or shading data is
obtained.
Following the reading operation of the reference white plate 22, an
image of an original document set on the contact glass 13 is read
by the first carriage 1 and the second carriage 2 like the
reference white plate 22. The data of the read image of the
original document is transmitted to the scanner control board 20
and is subjected to image processing. At this time, a white level
of image data of the read original document is corrected using the
shading data obtained by reading the reference white plate 22.
Thereby, an image output can be stabilized regardless of whether
there are variations in image output levels caused by the decrease
of the light amount of the exposure lamp 14 with time, etc.
Referring to FIG. 4, upon completion of image reading operation,
the stepping motor 8 starts rotating in the reverse direction so as
to return the first carriage 1 and the second carriage 2 to the
respective home positions. In order to return the first carriage 1
and the second carriage 2 to their respective home positions, as
much as possible, in the short time, the first carriage 1 and the
second carriage 2 are moved in a high speed. As described above,
the second carriage 2 moves in the sub-scanning direction at about
one-half of the moving speed of the first carriage 1.
When the home position sensor 12 detects the detection part 11
provided on the lower part of the first carriage 1, the first
carriage 1 and the second carriage 2 move by a predetermined
distance corresponding to predetermined pulses, and the stepping
motor 8 stops at the home position (i.e., the first and second
carriages 1, 2 stop at their respective home positions). The
stepping motor 8 waits at the home position until the stepping
motor 8 is driven for a next image reading operation of the image
reading device 50.
Next, an operation of the image reading device 50 in the
sheet-through mode will be described.
Referring to FIGS. 5A and 5B, in the sheet-through mode, a stack of
original documents are set on an original document tray (not shown)
of the document feeder 30. Upon pressing the start key (not shown),
the original document starts to be fed out from the original
document tray by a group of rollers provided in the document feeder
30. Simultaneously, the drive clock is output from the scanner
control board 20 to the stepping motor drive control board 21 at a
predetermined timing so as to drive the stepping motor 8.
Subsequently, the first carriage 1 and the second carriage 2 start
moving in the forward direction from their respective home
positions by driving the stepping motor 8. As illustrated in FIG.
5B, the first carriage 1 is accelerated to a predetermined
velocity.
Immediately after the first carriage 1 is accelerated to a
predetermined velocity, the motor drive electric current of the
stepping motor 8 is decreased such that the first carriage 1 moves
to a position where the reference white plate 22 is provided,
thereby decelerating the first carriage 1.
That is, the deceleration of the first carriage 1 is started in a
velocity transitionary period from an acceleration to a constant
velocity period.
After a predetermined time has passed since the decrease of the
motor drive electric current of the stepping motor 8, the
vibrations of the first carriage 1 and the second carriage 2
decrease. That is, the friction loads of the first carriage 1 and
the second carriage 2 function as a brake when the carriages are
decelerated, thereby decreasing the load on the stepping motor 8.
Therefore, if the motor drive electric current is decreased when
reading the reference white plate 22, the vibrations of the first
carriage 1 and the second carriage 2 decrease.
When the vibrations of the first carriage 1 and the second carriage
2 decrease, the reading operation of the reference white plate 22
is started. Due to the decrease of the vibrations of the first
carriage 1 and the second carriage 2, the reference white plate
reading operation can be performed stably. Specifically, the
surface of the reference white plate 22 is irradiated with a light
of the exposure lamp 14. The first mirror 15 reflects the light
reflected from the surface of the reference white plate 22.
Further, the second mirror 16 and the third mirror 17 sequentially
reflect the light reflected from the first mirror 15. The light
reflected from the third mirror 17 is led to the CCD 19 through the
imaging lens 18, and the reflected light is converted into an
electric signal by the CCD 19.
The data of the reference white plate 22 obtained by the CCD 19 is
transmitted to the scanner control board 20 and is subjected to
image processing. Consequently, a reference white level or shading
data is obtained. The shading data is used for correcting a white
level of image data of a read original document. By such a
correction of the white level of image data of the read original
document, an image output can be stabilized regardless of whether
there are variations in image output levels caused by the decrease
of the light amount of the exposure lamp 14 with time.
As illustrated in FIG. 5B, when the reading operation of the
reference white plate 22 is completed, the first carriage 1 still
moves in a decelerated condition. In order to stop the first
carriage 1 and the second carriage 2 in the short time, the drive
electric current for driving the stepping motor 8 is increased
immediately after the completion of the reference white plate
reading operation, and the first carriage 1 and the second carriage
2 are controlled to be rapidly decelerated and stopped. In this
deceleration control operation, because the reference white plate
reading operation is already completed, there is no serious
influence even if the first carriage 1 and the second carriage 2
vibrate to some extent. Further, the first carriage 1 and the
second carriage 2 can be stopped in the short time, so that the
whole period of time required for performing the reading operation
of the reference white plate 22 can be reduced.
Immediately after the first carriage 1 and the second carriage 2
have stopped, the first carriage 1 and the second carriage 2 are
driven to move in the return direction indicated by the arrow in
FIG. 5A. When the first carriage 1 moves to the "image reading
position in the sheet-through mode," the first carriage 1 and the
second carriage 2 stop moving. With regard to the return speed of
the first carriage 1 toward the "image reading position in the
sheet-through mode," in order to reduce the vibrations of the first
carriage 1 as much as possible until the start of an image reading
operation of an original document which is performed immediately
after the stop of the first carriage 1, the first carriage 1 is
driven to move at a lower speed than the moving speed of the first
carriage 1 when the first carriage 1 moves to the reference white
plate 22 for reading.
At the "image reading position in the sheet-through mode," an image
of an original document fed out from the original document tray by
a group of rollers provided in the document feeder 30 is read by
the first carriage 1 and the second carriage 2. Similarly in the
image reading system moving mode, the reflected light from the
image surface of the original document is led to the CCD 19 through
the imaging lens 18. The reflected light is converted into an
electric signal by the CCD 19. The data of the read image of the
original document obtained by the CCD 19 is transmitted to the
scanner control board 20 and is subjected to image processing. At
this time, a white level of image data of the read original
document is corrected using the shading data obtained by reading
the reference white plate 22. Thereby, an adequate image output can
be obtained.
Because the image reading operation of the original document is
performed in a condition that the vibrations of the first carriage
1 are reduced as much as possible, an inferior image reading at the
tip portion of the image of the original document due to vibrations
of the first carriage 1 is typically prevented. Therefore, an image
of an original document can be read with accuracy in the image
reading device 50.
As described above, in the image reading device 50 according to the
embodiment of the present invention, the deceleration of the first
carriage 1 is started in a velocity transitionary period from an
acceleration to a constant velocity period, and the reading
operation of the reference white plate 22 is performed in the
decelerated condition of the first carriage 1. As compared to the
reading operation of the reference white plate performed in the
area "A" in FIG. 7 according to the background art, the reading
operation of the reference white plate 22 starts earlier in the
image reading device 50. As a result, the whole period of time
required for performing the reading operation of the reference
white plate can be reduced.
Further, as compared to the reading operation of the reference
white plate performed in the area "B" in FIG. 7 in which the
carriage is accelerated according to the background art, the
reading operation of the reference white plate 22 can be performed
stably in a decelerated condition in which vibrations of the
carriage are less than those in an accelerated condition.
Therefore, the reference white plate 22 can be read with accuracy
in the image reading device 50.
Next, another embodiment of the present invention will be described
referring to FIG. 6, in which the above-described image reading
device 50 is used in an image forming apparatus, such as a copying
machine.
FIG. 6 is a schematic vertical longitudinal sectional side view of
a copying machine according to another embodiment of the present
invention. A copying machine 60 includes the above-described image
reading device 50 serving as an image scanner at an upper part
thereof, and a printer device 61 that forms an image of an original
document read by the image reading device 50 on a sheet. In the
printer device 61, a sheet is fed to an electrophotographic printer
engine 64 through a sheet conveying path 67 from one of a sheet
feeding tray 62 that accommodates a stack of sheets therein and a
manual sheet feeding tray 63 that manually feeds sheets. The sheet
fed to the electrophotographic printer engine 64 is further
conveyed to a sheet discharging stacker section 66 via a fixing
unit 65 through the sheet conveying path 67.
In this embodiment, the electrophotographic printer engine 64
includes an organic photoreceptor 68, and a charging device (not
shown), an optical writing device 70, a developing device 71, and a
transfer device 72 arranged around the photoreceptor 68. The
printer device 61 further includes a sheet reversing mechanism 73
that reverses a sheet having an image on one side of the sheet.
An image is formed by the printer device 61 by an
electrophotographic image forming process. A brief description will
be made to an exemplary electrophotographic image forming process
of the printer device 61.
The image data of an original document read by the image reading
device 50 are sent to the printer device 61. The optical writing
device 70 converts the image data from the image reading device 50
into optical signals, and exposes a surface of the photoreceptor 68
uniformly charged by the charging device with the optical signals
to form an electrostatic latent image corresponding to the image of
the original document. The electrostatic latent image on the
photoreceptor 68 is developed with toner by the developing device
71.
A toner image on the photoreceptor 68 is transferred to a sheet fed
from one of the sheet feeding trays 62 and the manual sheet feeding
tray 63. Subsequently, the toner image on the sheet is fixed
thereonto by the fixing device 65. The sheet having the toner image
is discharged to the sheet discharging stacker section 66 as a copy
print.
The image forming apparatus such as the copying machine 60 can
achieve high performance such as high speed, high image quality,
etc., by employing the above-described image reading device 50.
In the above embodiment of the present invention, the image reading
device 50 is used in the copying machine 60 as an example of an
image forming apparatus. Alternatively, the image reading device 50
may be used in other similar image forming apparatus, such as a
facsimile machine.
Numerous additional modifications and variations of the present
invention are possible in light of the above teachings. It is
therefore to be understood that within the scope of the appended
claims, the present invention may be practiced otherwise than as
specifically described herein.
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